Mass measurement of the planets and their host stars is an essential precursor study for Roman Galactic Exoplanet survey. A big advantage if Keck is that it is also in IR just like Roman. In this talk I will demonstrate how this method has evolved over time with different events and measured really small separations to confirm that we can definitely measure most of them with Roman telescope. This study is also going to show the host mass dependence of the exoplanets which is very important since it will answer significant questions of planet formation.